Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Sustainable Earth https://doi.org/10.1186/s42055-020-00031-4

RESEARCH Open Access State level water security indices in Mexico Felipe I. Arreguin-Cortes1, J. Raul Saavedra-Horita2, J. Manuel Rodriguez-Varela3, Velitchko G. Tzatchkov3* , Petronilo E. Cortez-Mejia3, Oscar J. Llaguno-Guilberto3 and Arizabeth Sainos-Candelario3

Abstract Background: As tends to be the case in large, developing countries, Mexico is a nation of notable meteorological, hydrographic and social contrasts throughout its territory, which impact the various population strata in different ways. The public administration in Mexico is divided into federal (nationwide), state and municipal levels. In this sense, it is desirable to have water security metrics not only for the country as a whole but also for each state. The current paper seeks to show how these contrasts create different water-security scenarios using pertinent indices. This is particularly relevant for large countries such as Mexico, with approximately two-thirds of its territory in arid or semiarid areas, which face natural water scarcity, and only one-third has a very high relative water abundance. Results: The concept of the global water security index was adapted to the state level in Mexico and calculated for each Mexican state in accordance with the worldwide analysis methodology proposed by other authors, which considers water availability, accessibility, safety and quality, as well as management. The proposed methodology was applied in a geographic information system environment, and it was used to obtain water security indices for all Mexican states. The states in which the situation was found to be critical, according to the computed global index, are Sonora, Baja California and Guanajuato, followed by Mexico City, Colima, Aguascalientes and Sinaloa. Conclusions: Although the vast majority of the most vulnerable states and municipalities that have the highest drought risk are located in the north of the country in the Mexican highlands, even southern states such as Guerrero, Oaxaca, Chiapas, and Tabasco (which are typically characterized as rainy) have municipalities with a high drought vulnerability degree and are also severely affected by this phenomenon, especially in those years in which El Niño manifests itself, as was the case in 2015. The proposed methodology may serve as an example of how to assess water security using mainly free and officially published information, combined with international comparative country information, especially for countries where such information is limited. Keywords: Water security, Water availability, Access to water, Water management, Water resources in Mexico

Introduction from the impacts of hydrometeorological extremes and Several definitions have been proposed for the concept environmental deterioration. Among these methodolo- of water security by different authors [1–9], and various gies, [3] proposed a global water security index (GWSI) methodologies have been employed to express the con- to measure water security according to goal 6 of the 17 cept of water security via indices. As a common denom- global goals for sustainable development established by inator, the proposed definitions and their related the United Nations [10], namely, to ensure access to methodologies consider the availability and access to an water and sanitation for all. The GWSI is comprised of adequate quantity and quality of water for the popula- the following four criteria: availability, accessibility to tion and industry, along with an acceptable level of risk services, safety and quality, and management. The index proposed by [3] is applied at the global

* Correspondence: [email protected] (world) level, with country-scale data, transboundary 3Mexican Institute of Water Technology, Paseo Cuauhnahuc 8532, Col. river basin data, or data gathered from digital maps at a Progreso, 62550 Jiutepec, Morelos, Mexico low spatial resolution (0.5°), while the aggregated results Full list of author information is available at the end of the article

© The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 2 of 14

Table 1 Global water security index definition and data sources Criterion for Indicators Spatial and temporal scales Definition and data sources water security Availability WSI Spatial resolution: 0.5°; median WSI is defined as the relation between the total monthly values for 2010 water withdrawal and availability. Source: [11] Drought indicator (DI) Spatial resolution: 0.5°; annual values DI is calculated using hydrological model PCR-GLOBWB. for 2012 Source: [12] Groundwater depletion Spatial resolution: 0.5°; annual values Depletion is calculated using hydrological model PCR-GLOBWB. for 2010 Source: [13] Accessibility to Access to sanitation Country-scale data for 2014 Percentage of the population with access to sanitation. services Source: [14] Access to drinking water Country-scale data for 2014 Percentage of the population with access to drinking water. Source: [14] Safety and quality Water quality index Country-scale data for 2012 Includes 4 water quality parameters. Source: [15] Flood frequency index Country scale data for 1985–2003 Flood frequency. Source: [16] Management World governance index Country-scale data for 2010 Includes voice and accountability, political stability and absence of violence, government effectiveness, regulatory quality, rule of law, and control of corruption. Source: [17] Transboundary legal Basin-scale data for 2015 Range of treaties per transboundary basin and their associated framework risks of conflict. Source: [18] Transboundary Basin-scale data for 2015 Level of tension in transboundary basins and the associated hydropolitical tension risk levels. Source: [18] have a resolution of 5′ (approximately 10–15 km at the developing cities where the combination of high socio- intermediate latitudes). Table 1 lists the criteria, indica- economic pressures (e.g., rapid population growth, tors, scales, definitions and data sources used in [3]. This slums, low GDP, and polluting industries) and inad- index is a good starting point for monitoring the pro- equate responses (weak institutions and poor planning gress towards the United Nations sustainable develop- and operational management) leads to the inappropriate ment goals and identifying strategies to improve the fulfilment of most functions of the urban water system. capability of nationwide as well as transboundary institu- Makin et al. [21] integrated an index that considers tions. A higher spatial resolution is needed to define five water security dimensions, i.e., domestic, economic, specific improvement needs and measures to be imple- urban, environmental and disaster resilience, and applied mented within each country. However, this is particu- it to 7 countries in Asia and 13 countries in America, larly relevant for large countries such as Mexico, with Africa and Europe, with no conclusive results. Shresthaa approximately two-thirds of its territory in arid or semi- et al. [22] developed a water security index to arid areas, which face a natural water scarcity, while only characterize the actual field conditions using a model one-third has a very high relative water abundance. centered on household water-use behavior in urban A watershed sustainability index, which integrates so- areas of developing countries, which can be used to de- cial, economic and environmental impacts using a sign policies and programs in small communities in such pressure-state-response model, was proposed in [19] and countries. Assefa et al. [23] noted that water security in- applied to a 2200 km2 basin in Brazil, thereby obtaining dices have been developed at the global, regional and a value of 0.65, which represents an average sustainabil- country levels but that there is a clear absence of indices ity value for the basin. Using a pressure-state-impact-re- at the domestic level, considering the water supply, sani- sponse model, van Ginkel et al. [20] developed a tation and hygiene. Using 12 indicators, they developed dashboard of 56 indicators to establish a water security an index that was applied to the city of Addis Ababa, index and applied the index to ten cities. In their ap- Ethiopia. The water supply dimension was found to be proach, the highest water security levels were obtained at a good level, whereas the sanitation and hygiene di- in wealthy cities in water-abundant environments, in mensions were poor and fair, respectively, concluding which security is determined by the ability of the city to that the index can be a useful tool for water utilities. mitigate flood risks and to sustain the hinterland water The public administration in Mexico is divided into fed- supply dependency, as opposed to the lowest security in eral (nationwide), state and municipal levels. In this sense, Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 3 of 14

it is desirable to have water security metrics not only for Scarcity index the country as a whole but also for the states. Several stud- The water scarcity index (WSI) is determined by the ies have been devoted to water security in Mexico. In [4], sustainable or renewable supply, the environmental flow the trends of demographic growth, urbanization, demand requirements, and the demand for all purposes, such as for energy and food, climate change and water manage- public, urban, rural, industrial, agricultural, livestock and ment in Mexico were analyzed, whereby recommenda- other purposes. The methodology uses WSI defined as tions were formulated with a particular focus on water the relationship between the total water withdrawal and security centered on the urgency of achieving good water available water, considering the environmental flow re- management. Oswald Spring [24] examined water security quirements (Eq. 1). The available water includes renew- in Mexico, based on social, political and economic aspects, able groundwater. The withdrawal element includes with a focus on the national water law that favors partici- surface and renewable groundwater that is used in agri- pation in developing an integrated management model, culture and industry as well as in homes. Nonetheless, which compares the current water use among different so- the use of nonrenewable groundwater, in other words, cial and productive sectors. Arreguín-Cortes et al. [25] its overexploitation, is not included in the water with- noted that Mexico faces various water security challenges, drawal but rather in a separate indicator [3, 26]. such as pollution, climate change, water scarcity, and management, and there exists the need to strengthen the W w WSI ¼ ð1Þ water-related science and technology in Mexico. However, Aw − Ew none of the authors above have defined and quantified specific water security indices. where Ww is the water withdrawal, Aw is the water avail- In the current work, the GWSI concept proposed in ability (renewable), and Ew represents the environmental [3] is adapted to the state level in Mexico as a first at- flow requirements. tempt to establish a benchmark using the standardized In the previous equation, the environmental flow re- method to report and compare the annual performance quirement Ew is calculated as Q90; in other words, the with a definition of the components and common inter- monthly stream flow that is exceeded 90% of the time. Al- national and national terminologies. In this way, not though it is better to determine this element using the de- only would nationwide (federal) stakeholders, water re- gree and nature of its dependency on the stream flow, sources management practitioners and decision-makers such information is rarely observed directly [3]. This fol- benefit from such tools but also those at the state level. lows the application of low-flow hydrology methods to Another reason to develop state-level water security in- river ecology and environmental flow management studies dices is information availability. Water governance in [27], and the method to estimate the environmental vol- Mexico follows a by-river-basin-council model so that ume on a global scale, as a percentage of the average an- the information regarding water availability and manage- nual runoff [28], is applied with the PCRaster GLObal ment is generated within river basin boundaries and is Water Balance (PCR-GLOBWB) hydrological model [11]. normally more easily extrapolated to the state level. To adapt the above at the state level in Mexico, the re- newable water Aw is considered to be the sum of the Methodology mean annual runoff Rw and the average aquifer recharge Mexico is a federation-type country composed of 32 states Gw [29]. Therefore, in its practical application, the envir- (the official country name is the United States of Mexico), onmental flow can be calculated as a certain percentage with very heterogeneous climatic and hydrographic charac- of the available renewable water (%Aw)or%Rw. The teristics. For each of these state entities, as an initial approxi- WSI can only vary between 0 and 100% since the use of mation, the GWSI was calculated in accordance with the nonrenewable groundwater is not included in the water methodology proposed by [3], although the index was origin- withdrawal. ally used at the global level. According to this methodology, In [28], Ew is estimated as 27% of the mean annual the GWSI consists of the following four indices, each with its runoff for central Mexico, 28% for the Rio Grande basin, own weight: availability, 45%; accessibility, 20%; safety and and 22% for north Mexico. The average Ew value is quality, 20%; and management, 15%. Official Mexican state- 25.6%, that is, Ew ≈ 0.256 Rw. There are recent Mexican scale data were employed for the water availability, accessibil- official data about the environmental flows (Ew as % Rw) ity, safety and quality indicators, while the data for the man- for some of the 37 hydrological regions (HRs) in the agement indicator were the same as those used in [3]. country and their basins, however, which are determined according to Mexican standard NMX-AA-159-SCFI- Availability 2012 [30] establishing the environmental flow determin- Water availability is determined according to scarcity ation procedure in hydrological basins. These are HR 12 (70%), droughts (15%) and groundwater depletion (15%). Lerma-Santiago [31], HR 14 Ameca River [32], HR 15 Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 4 of 14

Costa de Jalisco [33], HR 19 Costa Grande Guerrero Step 3. Calculation of the drought probability by means [34], HR 20 Costa Chica de Guerrero [35], HR 25 San of the envelope (D0 to D4), as the ratio between the Fernando [36], HR 28 Papaloapan [37], HR 30 Grijalva number of months with drought and the number of [38], and the Golfo and Pacífico Rivers [39]. For those records in the period. regions where such data were not found, an Ew value of Step 4. Classification of the probability of occurrence 30% was assumed, according to official Mexican recom- (degree of drought hazard). The probability values mendations [40] and the results from [28]. A matrix with oscillate within the closed range of [0, 1]. To classify the relationship between each of the Mexican states and these probabilities into percentiles with equal-sized cat- each of the HRs was then obtained, and average values egories, these values were adjusted to a normal distri- were calculated. For Tabasco, for example, an Ew average bution, and the result was multiplied by 100 to express of 55.6% was obtained, for Jalisco 48.9%, for Guerrero them as percentages. 49%, for Zacatecas 20.4%, etc. These results were applied to Rw for calculating the scarcity index. For 2015, at the Groundwater depletion 3 3 country level, Rw = 354,990 hm , Gw = 91,788 hm , and Groundwater depletion is determined according to the 3 Aw = 446,777 hm ,soGw ≈ 0.204 Aw [11]. natural recharge, the return flows from irrigation, and the annual groundwater extraction (for all purposes); if the annual groundwater extraction exceeds the natural Drought index recharge plus the runoff flows, this results in depletion. The drought index corresponds to hydrological Depletion is calculated as the ratio between the extrac- droughts, according to the drought frequency and aver- tion and natural recharge plus the return flows from irri- age frequency over a given period. To calculate the gation, which can generate a value higher than 1, so hydrological drought, the methodology uses the monthly normalization is required. The normalization method, 80th flow percentile, Q80, that is to say, the mean flow applied to the depletion values obtained from the extrac- that exceeds the monthly runoff 80% of the time [3]. In tion and recharge ratio from 0 to 1, is the Min-Max its application, a criterion can be used in which the method, as shown in Eq. 2 [43]: drought index is determined by the percentage of  drought-affected municipalities or by the percentage of t t xqc − minc xq0 state areas that was affected in the analysis period, in t ÀÁ ÀÁ Iqc ¼ t t ð2Þ this case from 2003 to 2017. maxc xq0 − minc xq0 In Mexico, the National Meteorological Service is the t official agency of the federal government responsible for where I qc is the normalized value of an individual indi- detecting the current status and evolution of drought cator q for a country (state) c in a given time period t t through the Mexico Drought Monitor [41]. This moni- and x qc is the gross value of the individual indicator q tor publishes monthly national maps of areas affected by for the country (state) c in time period t, with q =1, …, drought, according to an intensity scale comprising ab- Q and c = 1, ..., M. normally dry (D0), moderate drought (D1), severe drought (D2), extreme drought (D3), and exceptional Water access index drought (D4). In this index, access to drinking water carries a weight Thus, based on the historical records of the Drought of 60%, while access to sanitation has a weight of 40% Monitor of Mexico (2003 to 2017) for each category of [3]; see Eq. 3: drought and municipal data, in this work, the drought hazard was determined by calculating the probability of IAcce ¼ ðÞþ0:6 water ðÞÞð0:4 sanitation 3Þ drought occurrence (relative frequency) for each of the municipalities of Mexico, based on the methodology proposed by Ortega-Gaucin et al. [42], which consists of Water quality and protection against flooding the following steps: Water quality index To calculate this index, the methodology proposed by Step 1. Compilation of historical municipality records [3] uses the following five water quality parameters: with at least 40% of their territory affected by any drought intensity or drought conditions, from D0 to  Dissolved oxygen (DO) [mg/L] D4.  Electrical conductivity [microsiemens/cm] Step 2. Obtaining the absolute frequencies  pH [unitless] corresponding to each type of severity of drought by  Total phosphorous (P) [mg/L] municipality.  Total nitrogen (N) [mg/L] Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 5 of 14

8 BOD5 These parameters arose from consultations with ex- < 1; BOD5i; j ≤t PTT BOD perts and were obtained with available information from BOD5 ¼ BOD i; − t 5 i; j : − 5 j ; BOD > tBOD5 the UNEP GEMS/Water (the Global Environment Moni- 1 BOD 5i; j BOD5max − t 5 toring System for Water of the United Nations Environ- ð5Þ ment Programme), which occupies a unique position to monitor the inland water quality, as well as maintains a Winsorization was applied before employing Eq. 5, global water quality database called GEMStat, which has limiting the extreme values in the data to reduce the ef- millions of entries for lakes, rivers and groundwater sys- fect of possibly spurious outliers. tems that come from close to 3200 monitoring stations in more than 100 countries. Flood index (safety) The units of the five parameters are different; hence, The flood index expresses the flooding frequency for a they require normalization. Once normalized, they are given period, the same as in [3]. In Mexico, information considered of equal weight, and the results are aver- is available from public reports on hydrometeorological aged to obtain a global water quality index ranging phenomena per municipality for the period of 2000– from 0 to 1. Transformation of the results for the five 2016, published by CONAGUA [45]. The results require parameters is performed differently in each case using normalization, from 2003 to 2017 in our case, following the categorical scale method. In the case of the pH, the the same water quality criteria [15]. The safety (against raw data were converted into a proximity scale of flood) index S was computed with the following target values by Eq. 4 below in which the proximity to equation: target (PTT) indicates the target value; subindices i ! XN and j denote the state and monitoring station, respect- D =n ively, and max or min denotes the maximum or mini- S ¼ 1 ð Þ mum observed. The objective value of a parameter is N 6 denoted by t [15]: where D is the number of flood events per municipality 8 N > ; tPH ≤PH ≤tPH in each state, is the number of municipalities in the > 1 1 i; j 2 n > PH state, and is the number of years in the registered <> t − PHi; j − 1 ; PH < tPH period. PHPTT ¼ 1 tPH − PH i; j 1 ð Þ i; j 1 min 4 > PH The weights of the water-quality and safety indicators > PHi; j − t :> − 2 ; PH > tPH in the index are 50 and 50%, respectively, as shown in 1 PH − tPH i; j 2 max 2 Eq. 7:

ICS ¼ ðÞþ0:5C ðÞ0:5S ð7Þ The National Water Commission of Mexico (CON- AGUA by its initials in Spanish), nonetheless, does where C is the water-quality index and S is the index of not publish information related to the monitoring of safety against flooding. these five parameters. That is why in this study, infor- mation was used from the following four water- Water management quality parameters at the state level from 2015 that The water management index is comprised of the world are monitored by CONAGUA at 4999 sites around governance index with a weight of 70%, the transbound- Mexico [44]: ary legal framework (15%), and the hydropolitical trans- boundary tension (15%). This management index affects  The 5-day biochemical oxygen demand (BOD5) the other three criteria of the global water security index [mg/L] (availability, accessibility, and quality and safety). Primar-  Chemical oxygen demand (COD) [mg/L] ily, the world governance index is applicable at the coun-  Total suspended solids (TSS) [mg/L] try scale and evaluates voice and accountability, political  Total dissolved solids (TDS) [mg/L] stability and absence of violence, government effective- ness, regulatory quality, rule of law, and corruption The information from all 4999 CONAGUA stations control. was considered. As was the case in the methodology proposed by [15], normalization of these parameters, World governance index which have the same unit of measurement, mg/L, was The world governance index (WGI) [17] establishes that carried out in accordance with Eq. 5. In this case, subin- governance consists of the traditions and institutions by dices i and j denote the state and monitoring station, which authority in a country is exercised. This includes respectively. the process by which governments are elected, Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 6 of 14

monitored and replaced, the capacity of the government Environment Programme (UNEP) [46] for 286 trans- to effectively formulate and implement sound policies, boundary river basins that span 151 countries, among and the respect of citizens and the state for the institu- them Mexico. According to the TWAP methodology, tions that govern the economic and social interactions those values range from zero (very high risk) to 7 (very among them [17]. low risk). Table 2 summarizes the values corresponding Figure 1 defines the six variables of the world govern- to the Mexican border states, taken from the maps pre- ance index and shows its variation for Mexico, in per- sented in [46]. For the rest of the states (the nonborder centiles ranging from 0 to 100, from 2005 to 2015 [17]. states), a score of 7 is assumed, corresponding to a very Government effectiveness and regulatory quality in- low risk. creased slightly, but the other four indicators, voice and For normalization purposes, the values in Table 2 were accountability, political stability, absence of violence, rule divided by 7. of law, and control of corruption, decreased. In the absence of information disaggregated per Mexi- Transboundary hydropolitical tension (TT) can state for these 6 variables, their values were obtained Similarly, the TWAP hydropolitical tension indicator from [17] at the country level for 2015. Equal weighting narrows down the analysis to the formal provisions that was given to each of these variables in computing WGI. exist in transboundary basins to lessen the tensions aris- ing from the construction of water infrastructure—a Transboundary legal framework (LF) common source of dispute between countries—and fac- This indicator maps the presence of key international tors in other circumstances that could exacerbate trans- legal principles in transboundary treaties, providing a boundary hydropolitical tensions stemming from basin first overview of the set of principles underlying, at least development [46]. Its value ranges from 1 (very low risk) on paper, transboundary water relationships. The trans- to 5 (very high risk). boundary legal framework is based on the assumption Table 3 lists the values corresponding to the Mexican that the governance of a transboundary basin is guided border states, derived from the maps presented in [46]. by (among other things) the legal agreements in place For the rest of the states (the nonborder states), a score and that these agreements provide a framework for the of 1 is assumed, corresponding to a very low risk. allocation of resources for different uses between coun- The management index, according to the aggregation tries [46]. It is of clear importance for Mexico, a country of its three indicators and their weights, can be deter- that shares river basins and aquifers with other counties mined by Eq. 8: along its boundaries, namely, with the United States of America to the north and with Guatemala and Belize to IAd ¼ ðÞþ0:7 WGI ðÞþ0:15 LF ðÞð0:15 TT 8Þ its south. Values of the transboundary legal framework indicator, Table 4 and Fig. 2 explain the proposed conceptual along with those of the other indicators, are computed framework and process for obtaining the GWSI at the and published in the Transboundary Waters Assessment state level, which is in fact an adaptation of the method- Programme (TWAP) report of the United Nations ology described by [3] that integrates physical and

Fig. 1 World governance index from 2005 to 2015 for Mexico. Source: [17] Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 7 of 14

Table 2 Transboundary legal framework indicator for Mexican safety, mostly from 2015. For management, the same data border states. Source: [46] sources used by [3] were employed, although the govern- State Score (from 0 to 7) ance country level data are from 2015 instead of 2010. North boundary Then, the GWSI is calculated by aggregating the indica- Baja California 5.6 tors by simple additive weighting (SAW). The detailed adaptation procedure at the state level (instead of at the Sonora 3.5 country level) is described above in the respective sections Chihuahua 5.6 for each GWSI component. Coahuila 5.6 In the final result, the states were classified in water Nuevo León 5.6 security terms using the Jenks statistical clustering algo- Tamaulipas 5.6 rithm [47]. This algorithm identifies natural data group- South boundary ings to create classes that minimize the variability within each group and maximize the variability among groups Chiapas 1.345 in an attempt to create more homogeneous classes. The Tabasco 1.345 resulting classes are such that there is a maximum vari- Campeche 1.345 ance among the individual classes and the least variance Quintana Roo 0.19 within each class. QGIS software, in which the Jenks al- gorithm is incorporated, was used to establish the socioeconomic dimensions but with a particular data categorization. collection and processing approach used, including The weighting used is subjective; therefore, as recom- normalization and aggregation. Each of the four criteria mended in [3], in future practical applications of this of the GWSI, i.e., availability, accessibility, safety and adapted methodology, it is convenient to conduct valid- quality, and management, is in turn integrated by the in- ation meetings in each of the states, in which local ex- dicators shown in the flowchart in Fig. 2. Each indicator perts can formulate proposals for improvement, and criterion is weighted to express its relative contribu- including adjustments to the weights of all criterions tion to the GWSI. The same weights that were defined and their indicators. Although it is clear that availability by [3] were also used, as shown in the flow chart. The must be assigned the greatest weight, it is also true that highest relevance is assigned to the availability (45%), the management of water resources impacts its preserva- compared to the accessibility (20%), safety and quality tion, and therefore, it must be evaluated whether a man- (20%), and management (15%). agement weight of 15% is adequate. The data for each of the indicators are collected from different sources, and as the indicator values have different Handling and integration of the information in a GIS units of measurement, they are normalized from 0 to 1 to In light of the amount of data that has to be processed be compared with other indicators. Official annual data for the creation and mapping of the indices, it is neces- were used for the availability, accessibility, and quality and sary to use a geographical information system (GIS) that permits the capture, analysis, storage, consultation and presentation of data in reference to each state. The Table 3 Transboundary legal framework indicator for Mexican process was carried out using the open QGIS platform. border states. Source: [46] State Score (from 0 to 5) Results North boundary Figure 3 shows a map of the Mexican states in terms of Baja California 1.25 the GWSI calculated with the methodology in this study Sonora 2.00 as a first approximation based on the available data. The Chihuahua 1.25 states in which the situation is critical, according to the GWSI, are Sonora, Baja California and Guanajuato, Coahuila 1.25 followed by Mexico City, Colima, Aguascalientes and Nuevo León 1.25 Sinaloa. Tamaulipas 1.25 Table 5 lists, per Mexican state, its population, per- South boundary centage of urban area, and state marginalization de- Chiapas 4.00 gree (SMD) expressing the general economic Tabasco 4.00 condition of the state [48]. From the GWSI analysis, there are seven Mexican states with values between Campeche 4.00 0.46 and 0.52, which, according to the classification Quintana Roo 3.00 obtained, is considered a low GWSI index. These Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 8 of 14

Table 4 Hierarchy and weights for obtaining the state-level global water security index in our study Global water security index Availability Accessibility Safety and quality 20% Management 45% 20% 15% a) WSI (70%). a) Access to drinking water (60%). a) Water quality index (50%). Expresses social and institutional WSI ¼ Ww Percentage of the population with Includes the following four water- management issues such as water Aw − Ew where: access to sources of improved quality parameters monitored by planning and management, Ww: water withdrawal drinking water, i.e., installation of CONAGUA at 4999 sites around economic policies, and others. Aw: water availability (renewable) delivery points that protect water Mexico: BOD5, COD, TSS, and TDS a) World governance index (70%). and from external contamination, b) Flood index (50%). Includes voice and accountability, Ew: environmental flow particularly fecal contamination. Relative flooding frequency for a political stability and absence of requirements; in %Rw,as Includes piped water to homes, given period, whereby the violence, government effectiveness, determined by Mexican standard public hydrants, wells, protected information is available in public regulatory quality, rule of law, and NMX-AA-159-SCFI-2012, which es- springs, and rainwater collection reports on hydrometeorological control of corruption tablishes the procedure for environ- systems. phenomena per municipality b) Transboundary legal framework mental flow determination in b) Access to sanitation (40%). published by CONAGUA. (15%). hydrological basins. Percentage of the population with Expresses the range of treaties per b) Drought index (15%). access to improved sanitation transboundary basin and their As percentages of the municipalities (whereby human excretions are associated risks of conflict. with drought and of the state hygienically separated and is not c) Transboundary hydropolitical surface experiencing a drought, public, either private or shared). tension (15%). according to the Mexico Drought Includes discharge to sewers, septic Expresses the level of tension in Monitor. systems, discharge latrines, simple transboundary basins and the c) Groundwater depletion (15%). pit latrines or ventilated pit latrines. associated risk levels. Ratio of groundwater extraction to natural recharge plus return flows from irrigation.

states are Baja California, Sonora, Sinaloa, Colima, Ortega-Gaucin [50], are located in regions of Mexico Aguascalientes, Guanajuato and Mexico City. The that are most likely to suffer the effects of drought and population of these seven states is on the order of in which water availability has become a problem due to 26.08 million inhabitants, which represents approxi- the overexploitation of aquifers [49]. Mexico City, with a mately 21.7% of the total population of Mexico. It population close to 8.99 million inhabitants, and with should be noted that although the GWSI is low, the 41.02% of its total area of 1487.48 km2 urbanized, faces SMD in three of these states is also very low. the need to import water from other watersheds, thereby The states of Sonora, Baja California, Aguascalientes, becoming a low-GWSI urban area in Mexico. On the and Guanajuato, according to Arreguín-Cortes [49] and other hand, two of the states with the highest GWSI

Fig. 2 Flow chart of the proposed procedure for obtaining the global water security index and respective component weighting Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 9 of 14

Fig. 3 Global water security index at the state level

(Campeche, Chiapas, Nayarit, Oaxaca, San Luís Potosí, of this kind is beyond the scope of this paper and will be Tabasco and Yucatán) have a very high SMD, and in one considered in future work. Instead, at this stage of the of these states, the SMD is high. study, a simple sensitivity analysis was carried out with The urban area percentage provides a better interpret- respect to the weights of the four water security criteria. ation of the results since the north of Mexico has areas Numerical incremental analysis, also known as one-at-a- with greater territorial extension but a smaller portion of time (OAT) analysis [51], was employed by changing the urbanized area where water security must be guaran- one parameter at a time. The weight of one water secur- teed, which is favorable for water security. The states of ity criterion was incrementally changed to higher and Aguascalientes and Mexico City have larger problems lower values, while maintaining those of the others at with respect to their urban area; on the other hand, the their baseline (nominal) values. Thereafter, the weight states of Yucatan and Nayarit are those that have a was returned to its nominal value, and the process was higher water security and are home to a larger popula- repeated for each of the other inputs in the same way. tion with respect to their extension per state. For each individual weight change, the weights of the other three criteria were adjusted with the following Sensitivity analysis equation [52]: The GWSI value obtained by the proposed methodology − w0 depends on the weights assigned to each of the four 0 1 p w j ¼ w j ð9Þ water security criteria, which in turn depend on the wp weights assigned to their respective components (Fig. 2). The GWSI also depends on the component values them- where wj’ is the new weight, wp is the original weight of selves, which normally carry some level of uncertainty. the criterion to be adjusted and wp’ is the value after the While in the present paper the same weights as those criterion was adjusted. In this way, the sum of the used in [3] were assumed (i.e., 45% for availability, 20% weights was always equal to 100. Figure 4 depicts the for accessibility, 20% for safety and quality, and 15%, for graphical analysis results for the Mexican state of Aguas- management), mainly for comparison purposes, it is im- calientes. An increment of 5% was used. Table 6 lists the portant to investigate the capacity of GWSI to be robust weights used, above and below the nominal weights. to or independent of the arbitrary choice of the weights The input values for that particular Mexican state are and input data uncertainty. A detailed sensitivity analysis availability = 0.416, accessibility = 0.986, safety and Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 10 of 14

Table 5 Indicators per Mexican state No. GWSI range State Area (km2) Population (inhabitants) Percentage of the urban area SMD 1 Very high Campeche 57,679.11 902,250 0.450 High 2 Chiapas 73,594.23 5,228,711 0.729 Very high 3 Nayarit 27,771.26 1,188,671 1.016 Medium 4 Oaxaca 93,948.71 3,976,297 0.726 Very high 5 San Luis Potosí 60,462.75 2,723,772 0.743 High 6 Tabasco 24,701.82 2,400,967 0.625 Medium 7 Yucatán 39,663.36 2,102,259 1.857 High 8 Very low Aguascalientes 5559.73 1,316,032 3.148 Low 9 Baja California 73,565.74 3,348,898 1.291 Very low 10 Colima 5752.31 715,095 0.488 Very low 11 Ciudad de México 1487.48 8,985,339 41.022 Very low 12 Guanajuato 30,336.15 5,864,777 1.975 Medium 13 Sinaloa 56,801.37 2,977,104 1.099 Medium 14 Sonora 180,936.70 2,874,391 0.413 Low 15 High Durango 122,161.17 1,759,848 0.265 Medium 16 Guerrero 63,608.95 3,542,204 0.733 Very high 17 Hidalgo 20,653.08 2,862,970 1.379 High 18 Jalisco 77,952.90 7,880,539 1.542 Low 19 Michoacán de Ocampo 58,300.20 4,599,104 1.496 High 20 Quintana Roo 42,659.91 1,505,785 1.212 Medium 21 Tlaxcala 3981.92 1,274,227. 1.618 Medium 22 Veracruz 71,470.07 8,127,832 1.344 High 23 Low Chihuahua 246,972.63 3,569,479 0.492 Low 24 Coahuila de Zaragoza 150,670.31 2,961,708 2.256 Low 25 México 22,227.39 16,225,409 4.848 Low 26 Morelos 4861.89 1,912,211 6.667 Medium 27 Nuevo León 63,615.16 5,131,938 1.657 Very low 28 Querétaro 11,603.60 2,043,851 1.984 Low 29 Medium Baja California Sur 73,964.04 718,384 0.370 Low 30 Puebla 34,119.27 6,183,320 1.876 High 31 Tamaulipas 79,404.09 3,453,525 1.216 Low 32 Zacatecas 74,502.48 1,581,575 0.479 Medium

quality = 0.700, and management = 0.577. For those Discussion values and the nominal criterion weights (45% for avail- In this work, the methodology proposed in [3] for ability, 20% for accessibility, 20% for safety and quality, obtaining the global water security index was adapted to and 15%, for management), a GWSI of 0.614 is obtained, the state level in Mexico, with data mainly from CONA- and the results in Fig. 4 deviate from that value for each GUA, as well as international data for the management incremental weight variation. The GWSI is observed to component. The authors of [3] propose that the index deviate by less than 7%, demonstrating that the index is can be applied at the global scale so that the water se- robust with respect to changes in the weights. As shown curity performance of each country can be determined, in the figure, the sensitivity is higher for the availability thus establishing a worldwide water security benchmark and accessibility components, explained by the high that can facilitate international cooperation. In this nominal weight of the former and the high (close to index, four criteria or interrelated physical and socioeco- one) value of the latter. nomic factors with prioritized attention are contained, Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 11 of 14

Fig. 4 Sensitivity analysis for the state of Aguascalientes namely, water availability, access to sanitation and Coahuila, Durango, the northern part of Nuevo León drinking water, safety against extreme hydrometeoro- and Tamaulipas), central west (Nayarit, Jalisco, Michoa- logical events, and management. Within the manage- cán, and Guanajuato), and the southeast (Tabasco, Chi- ment criterion, there is a world governance index apas, Yucatán, Campeche and Quintana Roo). These composed of six indicators that vary in percentile results coincide with historical drought logs since states range from 0 to 100. in the national territory that have historically been more The water quality parameters employed in the present affected by droughts are located in the Mexican high- study for computing the water quality index are different lands. These states experience the aggravated effect of from those used in [3, 15], mainly because the water being located in zones that are characterized by being quality parameters used in [3] are not monitored and of- preeminently arid, which is why their populations and ficially published in Mexico. No attempt has been made distinct economic activities are highly vulnerable due to to analyze how close the results would be to those ob- the water scarcity provoked by droughts, given that in tained by the methodologies in [3, 15]. While this could the majority of these states, extremely dry and semidry be examined in future work, the water quality index climates predominate. Although the vast majority of the computed in the present study uses data from 4999 sta- most vulnerable states and municipalities that have the tions across Mexico (the index proposed in [3] uses data highest drought risk are found in the north in the from 3200 stations around the globe), thus being coun- Mexican highlands, even southern states such as try specific and more representative for the study Guerrero, Oaxaca, Chiapas, and Tabasco (which are typ- purposes. ically characterized as being rainy) contain municipalities The Mexican states that have a higher probability of that have a high degree of drought vulnerability and are being affected by drought are those found in the north- also severely affected by this phenomenon, especially in west of Mexico (Baja California, Baja California Sur, those years in which El Niño manifests itself, as was the Sonora, and Sinaloa), in the central north (Chihuahua, case in 2015. That year, many municipalities in Chiapas Guerrero, Oaxaca and Tabasco, mainly, had declared a Table 6 Weights used in the sensitivity analysis state of emergency due to drought, and the agriculture and livestock sectors experienced significant losses. Variation Availability Accessibility S&Q Management Water security is transversal in every aspect of eco- 15% 60% 35% 35% 30% nomic development. People assign meaning to the con- 10% 55% 30% 30% 25% cept of water security depending on the scale and the 5% 50% 25% 25% 20% particular context in which it is applied. Water security 0% 45% 20% 20% 15% can never be fully reached because physical and eco- −5% 40% 15% 15% 10% nomic conditions are in constant flux, which requires constant adaptation [53]. There is no single solution to −10% 35% 10% 10% 5% increase water security. Moreover, solutions must be −15% 30% 5% 5% 0% adapted to the local conditions of each country, basin, Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 12 of 14

city, project or administration area. Water security and treatment, improved drinking water services, etc.—ac- integrated water resources management (IWRM) are tions that directly strengthen water security in Mexico. symbiotic: the adaptive management policies contained For the application of the GWSI at the state level, there in IWRM help to improve water security from the na- is annual information available mainly from CONAGUA, tional level to the local level. Water security should be as well as international data in the management compo- seen as the goal of IWRM; that which cannot be mea- nent. The main difficulty in integrating aspects such as sured, cannot be managed, and thus water security water governance, institutional (effectiveness) coordin- measurement is fundamental to its enhancement. ation and environmental water requirements lies in the The task of improving water security implies respond- lack of information and monitoring of those variables ing not only to the risks that are observed in the present that normally are not measured in Mexico. It would be but also adequately responding to the new challenges desirable to determine such indicators, available at the that occurring in the sector. Known challenges to over- country level, for each of the states. The future chal- come in reaching water security are water scarcity, water lenges include obtaining relevant real and documented pollution, adverse effects of hydrometeorological events, information for the different levels of government, as growing water conflicts and environmental deterioration well as an authority responsible for the monitoring and of basins and aquifers [1–9, 24, 25]. The methodology recording of institutional coordination and effectiveness, proposed in this paper, applied at the state level in a role that could be fulfilled by river basin councils. Mexico, contributes to a better understanding of the im- Finally, the methodology proposed in this paper may plications of water security and has a high potential to serve as an example of how to assess water security, at track changes over time to inform IWRM practices and least as a first approximation, using mainly free and offi- define public policies. cially published information, combined with inter- In this first study on water security indices in Mexico, national comparative country information, especially for the environmental flow volume was obtained mainly countries where such information is limited. according to a custom official Mexican standard that es- Abbreviations tablishes the procedure for environmental flow determin- BOD5: 5-day biochemical oxygen demand; COD: Chemical oxygen demand; ation in hydrological basins, named NMX-AA-159-SCFI- CONAGUA: National Water Commission of Mexico (from Comisión Nacional 2012 [30]. The simple recognition in that norm whereby de Agua in Spanish); DO: Dissolved oxygen; GIS: Geographical information system; GWSI: Global water security index; HR: Hydrological region; the environmental water requirements between basins de- IWRM: Integrated water resources management; LF: Transboundary legal pend on the context of both the water demand and eco- framework; PCR-GLOBWB: PCRaster GLObal Water Balance hydrological logical importance represents, in fact, a major Mexican model; PTT: Proximity to target; TDS: Total dissolved solids; TSS: Total suspended solids; TT: Transboundary hydropolitical tension; advance towards water security. In future work, the appli- TWAP: Transboundary Waters Assessment Programme; UNEP: United Nations cation of other approaches, for example, the one proposed Environment Programme; UNEP GEMS: United Nations Environment in [54], which considers more updated environmental Programme Global Environment Monitoring System; WGI: World governance index; WSI: Water scarcity index water science and management approaches, can also be assessed. Acknowledgements Not applicable.

Conclusions Authors’ contributions The main limitation for the construction of an index Felipe I. Arreguín Cortés and J. Raúl Saavedra Horita participated in the that adheres to the reality of Mexico and clearly reflects Project conceptualization. Velitchko G. Tzatchkov and Petronilo E. Cortez Mejía developed the proposed methodology. J. Manuel Rodríguez Varela the national situation is the lack of information. In this and Velitchko G. Tzatchkov did the investigation. Velitchko G. Tzatchkov area, there is an absence of measurement, follow-up and drafted the manuscript. Óscar J. Llaguno Guilberto developed the GIS data processing, asymmetrical information at different software application and visualization. Arizabeth Sainos Candelario participated in the data curation. All authors read and approved the final aggregate levels (state and municipal), and discretional manuscript. handling of existing information. On the other hand, a complication of information integration is determining Funding the degree of benefit attributed to water security given Not applicable. This research received no external funding. the complexity of the problem. Availability of data and materials In regard to the components that were analyzed to The datasets supporting the conclusions of this article are directly accessible, create the management indicator, it can be conclusively in an interactive way, on the http://172.16.2.211/ish/ homepage and public repository. stated that they are implicit within the considered indi- cators and occur in transversal form. In the future, it is Ethics approval and consent to participate recommended to incorporate information relative to the Not applicable. authorized budgets and their effective employment in Consent for publication states related to flood control, droughts, water Not applicable. Arreguin-Cortes et al. Sustainable Earth (2020) 3:9 Page 13 of 14

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